Methods, systems, and computer readable media for utilizing a jamming-resistant receiver device

ABSTRACT

A method for utilizing a jamming-resistant receiver (JrRx) device includes receiving, by a BJM engine, a plurality of individual subcarrier signals that comprises separate signal portions of a combined signal stream, wherein the combined signal stream is a combination formed by a source signal stream from a sender device and one or more interfering jamming signals from a plurality of unknown jammer devices and computing, by the BJM engine, a respective plurality of BJM filters for the plurality of individual subcarrier signals in the absence of channel information corresponding to the interfering jamming signals. The method further includes applying, by the BJM engine, the plurality of BJM filters to the respective plurality of individual subcarrier signals to decode data packets of the plurality of individual subcarrier signals in order to produce a plurality of source signal stream portions as decoded output, and recovering, by the BJM engine, the source signal stream by combining the decoded output from each of the plurality of BJM filters.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and claims priority to U.S. ProvisionalPatent Application Ser. No. 62/650,015, filed Mar. 29, 2018, thedisclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The subject matter described herein relates to wireless communicationsystems. More particularly, the subject matter described herein relatesto methods, systems, and computer readable media for utilizing ajamming-resistant receiver device.

BACKGROUND

As a critical concern of network security, radio jamming attacks inwireless networks have received a large amount of research efforts inthe past decades and have produced many insightful results regarding theattack destructiveness and defense mechanisms. Traditional anti-jammingapproaches include frequency hopping spread spectrum (FHSS) anddirect-sequence spread spectrum (DSSS). However, these approaches arenot capable of addressing powerful broadband jamming attacks and alsoresult in an inefficient spectrum utilization.

With the proliferation of wireless devices with multiple antennas,multiple-input and multiple-output (MIMO) has been adopted by themainstream anti-jamming solutions to salvage legitimate communicationsin jamming environments through spatial jamming mitigation at theauthorized users. For example, interference cancellation solutions havebeen developed to enable Wi-Fi communications in the presence of jammingsignals from home devices, such as a microwave oven and a baby monitor.A counter-jamming solution has also been developed by combiningmechanical antenna reconfiguration and digital signal processing.Similarly, an anti-jamming mechanism to defend against reactive jammerattacks in Wi-Fi communications has been proposed. However, the existingMIMO-based anti-jamming solutions greatly depend on the availability ofaccurate jamming channel information (e.g., channel ratio), which isdifficult to estimate in real-world wireless systems due to the lack ofknowledge of jamming signals. Therefore, the existing M IMO-basedanti-jamming solutions are not amenable to practical implementation inreal-world wireless systems, especially in multi-jammer environments.

SUMMARY

This Summary lists several embodiments of the presently disclosedsubject matter, and in many cases lists variations and permutations ofthese embodiments of the presently disclosed subject matter. ThisSummary is merely exemplary of the numerous and varied embodiments.Mention of one or more representative features of a given embodiment islikewise exemplary. Such an embodiment can typically exist with orwithout the feature(s) mentioned; likewise, those features can beapplied to other embodiments of the presently disclosed subject matter,whether listed in this Summary or not. To avoid excessive repetition,this Summary does not list or suggest all possible combinations of suchfeatures.

In some embodiments, the presently disclosed subject matter includes amethod for utilizing a jamming-resistant receiver (JrRx) device includesreceiving, by a BJM engine, a plurality of individual subcarrier signalsthat comprises separate signal portions of a combined signal stream,wherein the combined signal stream is a combination formed by a sourcesignal stream from a sender device and one or more interfering jammingsignals from a plurality of unknown jammer devices and computing, by theBJM engine, a respective plurality of BJM filters for the plurality ofindividual subcarrier signals in the absence of channel informationcorresponding to the interfering jamming signals. The method furtherincludes applying, by the BJM engine, the plurality of BJM filters tothe respective plurality of individual subcarrier signals to decode datapackets of the plurality of individual subcarrier signals in order toproduce a plurality of source signal stream portions as decoded output,and recovering, by the BJM engine, the source signal stream by combiningthe decoded output from each of the plurality of BJM filters.

In some embodiments, the presently disclosed subject matter alsoprovides a jamming-resistant receiver (JrRx) device comprising at leastone processor and memory. The JrRx device further includes a blindjamming mitigation (BJM) engine stored in the memory and when executedby the at least one processor is configured for receiving a plurality ofindividual subcarrier signals that comprises separate signal portions ofa combined signal stream, wherein the combined signal stream is acombination formed by a source signal stream from a sender device andone or more interfering jamming signals from a plurality of unknownjammer devices, computing a respective plurality of BJM filters for theplurality of individual subcarrier signals in the absence of channelinformation corresponding to the interfering jamming signals, applyingthe plurality of BJM filters to the respective plurality of individualsubcarrier signals to decode data packets of the plurality of individualsubcarrier signals in order to produce a plurality of source signalstream portions as decoded output; and recovering the source signalstream by combining the decoded output from each of the plurality of BJMfilters.

The subject matter described herein may be implemented in hardware,software, firmware, or any combination thereof. As such, the terms“function”, “module” or “engine” as used herein refer to hardware, whichmay also include software and/or firmware components, for implementingthe feature being described. In one exemplary implementation, thesubject matter described herein may be implemented using anon-transitory computer readable medium having stored thereon computerexecutable instructions that when executed by the processor of acomputer control the computer to perform steps. Exemplary computerreadable media suitable for implementing the subject matter describedherein include non-transitory computer-readable media, such as diskmemory devices, chip memory devices, programmable logic devices, andapplication specific integrated circuits. In addition, a computerreadable medium that implements the subject matter described herein maybe located on a single device or computing platform or may bedistributed across multiple devices or computing platforms.

An object of the presently disclosed subject matter having been statedherein above, and which is achieved in whole or in part by the presentlydisclosed subject matter, other objects will become evident as thedescription proceeds when taken in connection with the accompanyingdrawings as best described herein below.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram illustrating an exemplary wireless networkthat is subjected to jamming attacks;

FIG. 2 is a block diagram illustrating an exemplary signal jamming modelaccording to an embodiment of the subject matter described herein;

FIG. 3A-3B are graphs illustrating the performance of the BJM algorithmin various wireless network according to an embodiment of the subjectmatter described herein;

FIG. 4 is a block diagram illustrating an exemplary signal jamming modelin a multiple-input and multiple-output (MIMO) network according to anembodiment of the subject matter described herein;

FIG. 5 is a block diagram of an exemplary architecture of ajamming-resistant receiver (JrRx) device according to an embodiment ofthe subject matter described herein;

FIG. 6 is a diagram illustrating jamming signals and signal patternsaccording to an embodiment of the subject matter described herein;

FIG. 7 is a diagram illustrating a legacy Wi-Fi frame structureaccording to an embodiment of the subject matter described herein;

FIG. 8A is an image of an experimental setup in a testing environmentaccording to an embodiment of the subject matter described herein;

FIG. 8B is an image of the positioning of a sender device and jammerdevices in a testing environment according to an embodiment of thesubject matter described herein;

FIG. 8C is block diagram of an experimental setup in a testingenvironment according to an embodiment of the subject matter describedherein;

FIG. 9A is a block diagram illustrating an exemplary signal jammingmodel involving a single jamming device in a multiple-input andmultiple-output (MIMO) environment according to an embodiment of thesubject matter described herein;

FIG. 9B is a block diagram illustrating an exemplary signal jammingmodel involving a pair of jamming devices in a multiple-input andmultiple-output (MIMO) environment according to an embodiment of thesubject matter described herein;

FIG. 9C is a block diagram illustrating an exemplary signal jammingmodel involving three jamming devices in a multiple-input andmultiple-output (MIMO) environment according to an embodiment of thesubject matter described herein;

FIG. 10 illustrates a plurality of graphs depicting the performance oftwo jamming-alleviation filters (JAF) in the synchronization algorithmat various transmitting powers according to an embodiment of the subjectmatter described herein;

FIGS. 11A-11D illustrate a plurality of constellation diagrams of thedecoded symbols at the JrRx device when subjected to different transmitpowers from the jammer device according to an embodiment of the subjectmatter described herein;

FIG. 12 illustrates a graph depicting the impact of jamming signalwaveforms on the performance of a JrRx device according to an embodimentof the subject matter described herein;

FIG. 13 illustrates a graph depicting the impact of jamming power fromone jamming device on the performance of a JrRx device according to anembodiment of the subject matter described herein;

FIG. 14 illustrates a graph depicting the impact of jamming power fromtwo jamming devices on the performance of a JrRx device according to anembodiment of the subject matter described herein;

FIG. 15 illustrates a graph depicting the impact of jamming power fromthree jamming devices on the performance of a JrRx device according toan embodiment of the subject matter described herein;

FIG. 16 is a block diagram of an exemplary jamming resistant receiverdevice according to an embodiment of the subject matter describedherein;

FIG. 17 is a flow chart depicting an exemplary method for utilizing ajamming-resistant receiver device according to an embodiment of thesubject matter described herein;

FIG. 18 is a block diagram of an exemplary wireless signal frame formataccording to an embodiment of the subject matter described herein; and

FIG. 19 is a block diagram of an exemplary architecture of ajamming-resistant receiver (JrRx) device according to an embodiment ofthe subject matter described herein.

DETAILED DESCRIPTION

The disclosed subject matter presents a practical anti-jamming solutionto salvage legitimate communications in wireless networks with multiplehigh-power and broadband radio jammers by leveraging MIMO signalprocessing techniques at the physical (PHY) layer, and evaluate thedisclosed solution on a wireless testbed consisting of USRP2 andGNURadio. In some embodiments, a blind jamming mitigation (BJM)algorithm is utilized and be configured to, cancel the jamming signalsfrom unknown jammers and recover the desired signals from a legitimatesender. Unlike other jamming mitigation algorithms that rely on theavailability of accurate jamming channel ratio, the BJM algorithm doesnot require any channel knowledge for jamming mitigation and signalrecovery.

Based on the BJM algorithm, a jamming-resistant receiver (termed JrRx)has been configured to decode data packets from a legitimate sender inthe face of interfering signals from multiple unknown jammers. In someembodiments, JrRx includes two key modules: a jamming-resilientsynchronization module and a BJM module. The core of each module is alinear spatial filter. Notably, JrRx is characterized by low complexity(e.g., linear operations without iterative decoding) and is thereforesuited for practical use. Based on JrRx, a holistic anti-jamming schemehas been implemented to enable legitimate communications in wirelessnetworks, such as Wi-Fi networks, cellular networks, and/or otherorthogonal frequency divisional multiplexing (OFDM) networks, whenattacked by multiple jammers. Notably, although the followingdescription may describe the JrRx receiver and/or the use of the BJMalgorithm in the context of a Wi-Fi network or Wi-Fitransmissions/communications, it is understood that the followingdescription pertains to any OFDM wireless network or communicationswithout deviating from the scope of the disclosed subject matter.

In some embodiments, JrRx may be implemented by using GNURadio-USRP2 ina Wi-Fi network with multiple jammers. Unlike prior works that use thepacket delivery rate as the performance metric, the disclosed matterutilizes the post signal-to-jamming-plus-noise ratio (pSJNR) of adecoded signal symbols to evaluate the performance of the JrRx. SincepSJNR determines the raw bit error rate (e.g., raw BER, BER withoutchannel code), it is more accurate to qualify the jamming mitigationcapability of the disclosed subject matter. Experimental results showthat (i) JrRx is robust to various jamming signals (e.g., full-spectrumjamming, half-spectrum jamming, single-frequency jamming, andrectangular-waveform jamming) and (ii) a JrRx device that is equippedwith more antennas than the jammers, it can successfully decode thesignals from the sender, even in the scenarios where the jamming signalsare 20 dB stronger than the desired signals.

The disclosed anti-jamming solution advances the state-of-the-art in thefollowing aspects: (i) unlike the prior solutions that require jammingchannel ratio, the disclosed subject matter does not require any channelknowledge, thereby making it suitable for practical use, (ii) thedisclosed subject matter solution can be used in both jamming andnon-jamming scenarios, thereby eliminating the requirement of jammingdetection, (iii) the disclosed subject matter solution is a holisticsolution, which includes not only jamming mitigation but alsojamming-resilient synchronization and carrier sensing components, and(iv) the disclosed subject matter can tackle multiple high-powerbroadband jamming attacks in real-world systems. Notably, this is thefirst practical anti-jamming solution that can handle multiplehigh-power broadband jamming attackers.

FIG. 1 is a block diagram illustrating an exemplary wireless network 100that is subjected to jamming attacks. For example, wireless network 100includes an access point (AP) 102 in communication with a group ofwireless user devices 104-108. In some embodiments, wireless network 100can include any orthogonal frequency divisional multiplexing network(OFDM) network, such as a Wi-Fi network, a cellular network, or thelike. For example, the data transmissions sent by wireless user devices104-108 may be conducted via OFDM modulation at the physical (PHY)layer, which is the case in most Wi-Fi networks (e.g., 802.11 ac andax), for example. Each wireless user device 102-108 is equipped withmultiple antennas. Carrier sense multiple access (CSMA) or its variationcan be used as the media access control (MAC) protocol to control themedia access among the wireless user devices 104-108.

In wireless network 100, there can exist one or more radio jammingdevices 110-112 (e.g., “jammers”). The jamming devices 110-112intentionally emit radio jamming signals into the air with the aim ofdisrupting the legitimate communications in wireless network 100. Insome embodiments, a number of assumptions on the jamming attacks can bemade. First, wireless user devices 102-108 have no knowledge of jammingdevices 110-112 or the jamming signals 114-116 transmitted by jammingdevices 110-112. This includes the number of jamming devices 110-112,the bandwidth and power of jamming signals 114-116, and the waveform ofjamming signals 114-116. Second, the bandwidth of jamming signals114-116 can be larger than, equal to, or less than the bandwidth oflegitimate signals 122-128. Notably, the spectrum of jamming signals114-116 can either fully or partially overlap with the spectrum oflegitimate signals 122-128. Third, jamming signals 114-116 can be anywaveform (e.g., OFDM signals, single-frequency signals,rectangular-waveform signals, and noise-like signals). Further, thesewaveforms of jamming signals 114-116 may vary over time. A fourthassumption is that the power of jamming signals 114-116 can be muchlarger than the power of legitimate signals 122-128 (e.g., 20 dBstronger). Lastly, each jamming device 110-112 can be a constant jammer(e.g., constantly emitting jamming signals), a random jammer (e.g.,randomly emitting jamming signals), or a reactive jammer (e.g.,intermittently emitting jamming signals). In addition to the aboveassumptions for the jamming attacks, the following assumptions forwireless user devices 104-108 can also be made. Notably, the number ofantennas at each wireless user device 104-108 is greater than or exceedsthe total number (or sum) of antennas at all jamming devices 110-112.Although the following description may describe ‘jamming signals’ and/or‘jamming devices’ as examples, it is understood that this disclosurepertains to any wireless OFDM based interference signal that interferesor “jams” a legitimate source signal from a sending device withoutdeviating from the scope of the disclosed subject matter. Notably, thejamming signal described herein may be any ‘interference signal’ thatoriginates from an “interfering device” that transmits a wireless signalthat inadvertently conflicts or interferes with the legitimate sourcesignal from the sending device. For example, the disclosed subjectmatter would operate the same (e.g., cancel the interference signal(s)and recover the source signal) regardless of whether theinterference/jamming signal was generated with the intent tojam/interfere with the original source signal or not.

In some embodiments, the disclosed subject matter includes a BJMalgorithm implemented in a jamming-resistant receiver (JrRx) device. Assuch, the JrRx device can enable successful communications in thepresence of multiple jammers as shown in FIG. 1. In some embodiments,the JrRx device may be implemented using GNURadio-USRP2 wireless testbedand evaluate its performance using experimental results.

FIG. 2 is a block diagram illustrating an exemplary signal jamming modelaccording to an embodiment of the subject matter described herein.Namely, FIG. 2 illustrates a wireless network 200 that includes onesingle-antenna sender device 202, one M-antenna receiver device 204, andK single-antenna jammer devices 206 _(1 . . . K). Network 200 can bedenoted as N (1, K, M). In network 200, the number of antennas 208_(1 . . . M) on the receiver device 204 is assumed to be is greater thanthe total number of antennas on the single-antenna jammer devices 206_(1 . . . K), i.e., M>K.

BJM in Narrow Band Network

In some embodiments, the developed BJM algorithm can be utilized in anarrow-band network. Namely, the process/algorithm described in thissection can be implemented by a blind jamming mitigation (BJM) engine(e.g., a BJM algorithm, module, and/or executable software) that isstored in memory and executed by one or more processors of a JrRx device(e.g., receiver device 204). Additional details regarding the BJM engineand JrRx device is described in greater detail below.

In some embodiments, H_(j) is denoted as the channel coefficient betweenthe sender device's antenna and the receiver device's jth antenna.G_(jk) is denoted as the channel coefficient between the antenna of thekth jammer device (e.g., jammer device 206 _(k)) and the jth antenna ofreceiver device 204. Further, X can be denoted as the original signal(e.g., the source signal) at the sender device 202 and Z_(k) is denotedas the jamming signal at the kth jammer 206 _(k). At receiver device204, Y=[Y₁, Y₂, . . . , Y_(M)]^(T) is denoted as the received signalvector, with Y being the signal from its jth antenna, while W=[W₁, W₂, .. . , W_(M)]^(T) is denoted as the noise vector, with W_(j) being thenoise from its jth antenna. Accordingly, Y_(j) may be calculated as:

${Y_{j} = {{H_{j}X} + {\sum\limits_{k = 1}^{K}{G_{jk}Z_{k}}} + W_{j}}},\mspace{14mu}{1 \leq j \leq M}$At receiver device 204, a linear spatial filter is employed to decodethe signal from sender device 202 in the presence of jamming signals.Here, the linear spatial filter may refer to a set of complex weightsthat can be used to combine the signal streams from different antennasat receiver device 204. In some embodiments, P is denoted as the linearspatial filter (e.g., a M×1 complex vector) and g is denoted as thedecoded (e.g., estimated) signal. Accordingly,{circumflex over (X)}=P ^(H) Ywhere the (⋅)^(H) operator represents the conjugate transpose. Based onthe above definition, the mean squared error (MSE) can be written as:MSE=

[|{circumflex over (X)}−X| ²]=

[|P ^(H) Y−X| ²]=P ^(H)

[YY ^(H)]P+

[XX ^(H)]−

[P ^(H) YX ^(H)]−

[XY ^(H) P],where

(⋅) represents the statistical expectation operator. Notably, the aboveequation is actually a quadratic function of P. To minimize MSE, thegradient can be taken with respect to P. The optimal filter P can beobtained by setting the gradient to zero, which can be shown as follows:

$\frac{\partial{MSE}}{\partial P} = {{2{{\mathbb{E}}\left\lbrack {YY}^{H} \right\rbrack}P} - {2\;{{\mathbb{E}}\left\lbrack {YX}^{H} \right\rbrack}}}$By setting

$\frac{\partial{MSE}}{\partial P}$to zero, an optimal filter can be obtained by:P=

[YY ^(H)]^(†)

[YX ^(H)]where the (⋅)^(†) operator represents the pseudo-inverse.

Notably, this equation represents the optimal design of P. To estimate

[YY^(H)] and

[YX^(H)] in P=

[YY^(H)]^(†)

[YX^(H)], the pilot signals (e.g., preamble or reference symbols) thatare widely available in wireless communication systems can be exploited.For example, L can be denoted as the number of pilot signals in thesystem. Further, [{tilde over (X)}(1), {tilde over (X)}(2), . . . ,{tilde over (X)}(L)] can be denoted as the pilot signals at senderdevice 202. Likewise, [{tilde over (Y)}(1), {tilde over (Y)}(2), . . . ,{tilde over (Y)}(L)] can be denoted as the received pilot signals at thereceiver device 204, which also includes jamming signals. Then, thestatistic expectation can be approached using the average operation overa set of pilot signals. Specifically,

[YY^(H)] and

[YX^(H)] are respectively estimated as follows:

${{\mathbb{E}}\left\lbrack {YY}^{H} \right\rbrack}:={\frac{1}{L}{\sum\limits_{l = 1}^{L}{{\overset{\sim}{Y}(l)}{\overset{\sim}{Y}(l)}^{H}}}}$${{\mathbb{E}}\left\lbrack {YX}^{H} \right\rbrack}:={\frac{1}{L}{\sum\limits_{l = 1}^{L}{{\overset{\sim}{Y}(l)}{\overset{\sim}{X}(l)}^{H}}}}$where the := operator represents value estimation. It should be notedthat {tilde over (Y)}(l) includes both the pilot signals from senderdevice 202 and the jamming signals from jammer devices 206. Based on theabove formulas for

[YY^(H)]J and

[YX^(H)], the filter P can be represented as:

$P:={\left\lbrack {\sum\limits_{l = 1}^{L}{{\overset{\sim}{Y}(l)}{\overset{\sim}{Y}(l)}^{H}}} \right\rbrack^{\dagger}\left\lbrack {\sum\limits_{l = 1}^{L}{{\overset{\sim}{Y}(l)}{\overset{\sim}{X}(l)}^{H}}} \right\rbrack}$where the superscript dagger symbol is a pseudo-inverse operator, {tildeover (X)}(l) is the pilot signals (e.g., reference signals) at thelegitimate sender (e.g., sender device 202) and {tilde over (Y)}(l) isthe received signal vector at the receiver (e.g., receiver device 204).Note that {tilde over (Y)}(l) includes signals from the legitimatesender device and the interference signals originating from the jammerdevices.

In some embodiments, an “Algorithm 1” can be embodied as an BJMalgorithm that executed by a BJM engine and may comprise two steps. Thefirst step includes (i) the receiver device and/or BJM engine computinga complex vector P using P=[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(Y)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(Y)}(l)^(H)]. The second step includes (ii) the receiver device employthe resulting complex vector P to decode the desired signals by:{circumflex over (X)}=P^(H)Y.

It is worth noting that the spatial filter P in P=[Σ_(l=1) ^(L){tildeover (Y)}(l){tilde over (Y)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over(Y)}(l){tilde over (Y)}(l)^(H)] has two functionalities: jammingmitigation and channel equalization. Namely, the filter P not onlymitigates the jamming signals, but the filter also equalizes the channelto recover the desired source signal from the sender device 202.

In some embodiments, filter P as calculated above is the core of the BJMalgorithm that is executed by a BJM engine. For example, as can be seenfrom P=[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(Y)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(Y)}(l)^(H)], the BJM algorithm executed by the BJM engine requires noknowledge of the jamming signals and/or the jamming devices. The BJMalgorithm only needs to have knowledge of the pilot (and/or reference)signals at the sender device 202. Due to these special properties, theBJM engine and/or the BJM algorithm is particularly suitable for jammingmitigation in practice.

From the derivation of P, the BJM algorithm can guarantee to yield theminimum MSE existing between the estimated and original signals. If thesender device 202 has sufficient pilot (reference) signals, then thefollowing lemmas regarding the performance of the BJM algorithm can beassumed to be true. For example, in Lemma 1, it can be assumed that innoise-negligible scenarios, the BJM algorithm can (i) completely canceljamming signals and (ii) perfectly recover the desired source signaloriginating from the sender device.

As proof for this lemma, consider network 200 in FIG. 2. Notably, H canbe denoted as the compound channel matrix between the transmitters(e.g., sender device 202 and jammer devices 206 _(1 . . . K)) and thereceiver device 204, which is a M×(1+K) complex matrix. The first columnof H is the channel vector between the sender device 202 and thereceiver device 204 and the (k+1)th column of H is the channel vectorbetween the kth jammer device 206 and the receiver device 204 (for1≤k≤K). Further, X can be denoted as the compound transmit signals atall transmitters (e.g., sender device and jammer devices), i.e., X=[X,Z₁, Z₂, . . . , Z_(K)]^(T). Then, the received signal vector at thereceiver device 204 can be written as Y=HX+W=HX, where the secondequation follows from the assumption that the noise is negligible.

When the sender device 202 has a sufficient number of pilot signals, theabove formulas for P are equivalent. For example:P=

[YY ^(H)]^(†)

[YX ^(H)]=[HR _(X) H ^(H)]^(†)[HD _(X)]where R_(x) is X's autocorrelation matrix and D_(X)=[σ_(X) ², 0, 0 . . ., 0] with σ_(X) ² being X's variance.

X̂ = P^(H)Y = P^(H)HX = ([HR_(X)H^(H)]^(†)[HD_(X)])^(H)HX = (H^(H)[HR_(X)H^(H)]^(†)[HD_(X)])^(H)X = [1  0  …  0]X = X.Recall that {circumflex over (X)} represents the estimated signal at thereceiver device 204 and X is the original signal at the sender device202. The above equation indicates that the jamming signals can becompletely cancelled by the BJM engine, and the desired source signalfrom sender device 202 can be perfectly recovered.

In some embodiments, Lemma 1 demonstrates the superior performance ofthe BJM algorithm and/or BJM engine in noise-negligible scenarios. Inthe scenarios where the noise is not negligible, it is difficult toanalytically qualify the performance of the BJM algorithm. Hence,simulation can be utilized in these instances.

FIG. 3A-3B are graphs illustrating the performance of the BJM algorithmin various wireless network according to an embodiment of the subjectmatter described herein. For example, FIG. 3A illustrates a graph 302that depicts the performance of the BJM algorithm in a N(1, 1, 2)network. Likewise, FIG. 3B illustrates a graph 304 that depicts theperformance of the BJM algorithm in a N(1, 2, 3) network. In each ofFIGS. 3A and 3B, the x-axis represents the jamming-to-signal ratio (JSR)before the application of BJM processing and the y-axis represents thesignal-to-jamming-plus-noise ratio (SJNR) after BJM processing. Notably,in all of the noise scenarios (e.g., SNR 0 dB, 10 dB, 20 dB, or 30 dB)when the JSR increases from −60 dB to 100 dB, the SJNR degradation isless than 5 dB in N(1, 1, 2) as shown in graph 302 of FIG. 3A and lessthan 7 dB in N(1, 2, 3) as shown in graph 304 of FIG. 3B. This dataindicates that the BJM algorithm is extremely effective in jammingmitigation in each of a low, mid-, and high-SNR scenario.

In some embodiments, the BJM algorithm involves matrix multiplicationand pseudo-inverse manipulations. All of these manipulations are linearoperations. In some embodiments, the dimension of the matrix includesthe number of antennas at the receiver, which is typically small (e.g.,less than or equal to eight in 802.11ac). Thus, the complexity of theBJM algorithm is very low and acceptable in real-world wireless systems.

BJM Algorithm in OFDM-MIMO Broadband Network

The disclosed BJM algorithm was developed based on the simplifiedjamming model illustrated in FIG. 2, where each sender device 202 andjammer device 206 has a single antenna. In contrast, FIG. 4 demonstratesa scenario where the BJM engine and/or BJM algorithm can be used in aMIMO network 400 that includes a sender device 402 comprising aplurality of antennas 410 _(1 . . . Q) and receiver device 404comprising a plurality of antennas 408 _(1 . . . M). MIMO network 400further includes a plurality of jammer devices 406 _(1 . . . K) that maysimilarly comprise multiple antennas 412 _(1 . . . N). In someembodiments where the sender device 402 has multiple antennas 410_(1 . . . Q), sender device 402 may use its multiple antennas 410_(1 . . . Q) for spatial diversity and send one data stream to receiverdevice 404. This diversity mode is supported by all Wi-Fi standards. Inthis mode, sender device 402 with multiple antennas 410 _(1 . . . Q) canbe viewed as a sender with a single combined antenna according to theMIMO theory. Therefore, the BJM algorithm can be used by a BJM engine inMIMO network 400 where the sender device has multiple antennas.Likewise, one or more of jammer devices 406 _(1 . . . K) can includemultiple antennas. In the context of blind jamming mitigation, a jammerdevice 406 with N antennas can be treated as N independentsingle-antenna jammers. Therefore, the BJM algorithm executed by a BJMengine can be used in MIMO network 400 where each jammer device hasmultiple antennas. As such, as long as the number of antennas at awireless user device (e.g., the receiver device 404) is greater than thetotal number of antennas at jammer devices 406 _(1 . . . K), thereceiver device 404 can successfully decode the signals from themulti-antenna sender device 402.

In order to support high-rate data transmission in a broadband MIMO-OFDMnetwork (e.g., M IMO network 400 as shown in FIG. 4), the broadbandchannel is divided by the JrRx device into many narrow-band channelsusing OFDM modulation. For example, each OFDM subcarrier (e.g., a radiofrequency subcarrier wave) corresponds to a narrow-band channel. Tohandle the jamming attacks in a broadband network, the BJM algorithm (asspecified in “Algorithm 1”) is applied to each of the OFDM subcarriers.Specifically, for the signals on each individual subcarrier, a BJMengine can be configured to utilize P=[Σ_(l=1) ^(L){tilde over(Y)}(l){tilde over (Y)}(l)]^(†)[Σ_(l=1) ^(L){tilde over (Y)}(l){tildeover (Y)}(l)^(H)] to compute the subcarrier's BJM filter and then use{circumflex over (X)}=P^(H)Y to decode its desired signal at thereceiver.

FIG. 5 is a block diagram of an exemplary architecture of ajamming-resistant receiver (JrRx) device according to an embodiment ofthe subject matter described herein. Based on the BJM algorithm and/orBJM engine, a JrRx device that decodes its desired signals in thepresence of jamming signals can be designed. For example, FIG. 5 showsthe architecture of a JrRx device 500, which includes a radio frequency(RF) front-end component 502, a synchronization engine 504, a fastFourier transform (FFT) module 506, and a BJM engine 508. Compared to atypical multi-antenna receiver, JrRx device 500 does not need anyhardware based modifications. The JrRx device 500 instead needs abaseband signal processing algorithm upgrade. As shown in FIG. 5, JrRxdevice 500 includes comprises at least a synchronization engine 504 andthe BJM engine 508. In some embodiments, BJM engine 508 is configured toconstruct or generate one or more BJM filters for a respective one ormore subcarriers. For example, the BJM filter (e.g., a vector of complexnumbers) can be generated by the BJM engine 508 using P=[Σ_(l=1)^(L){tilde over (Y)}(l){tilde over (Y)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tildeover (Y)}(l){tilde over (Y)}(l)^(H)]. Notably, each constructed BJMfilter can be used (e.g., applied by BJM engine 508) on each individualsubcarrier to mitigate jamming or interference signals in such a mannerthat the desired source signal from the sender is recovered at the JrRxdevice. The BJM filter is directly calculated by BJM engine 508 usingthe interfered reference signals in the data packet. The calculation byBJM engine 508 of the BJM filter on a subcarrier may use the referencesignals on that subcarrier and on its neighboring subcarriers. Notably,the calculation of BJM filters by BJM engine 508 does not require theknowledge of the channels between the sender/jammers and the receiver.

In some embodiments, synchronization engine 504 in JrRx device 500 hastwo functionalities: timing synchronization and frequencysynchronization. Timing synchronization includes searching by engine 504for the start of each frame by exploiting auto or cross correlation ofthe signal stream in the time domain. Likewise, frequencysynchronization can be conducted by engine 504, which can estimate andcorrect the frequency offset between a sender device and a receiverdevice.

Notably, performing synchronization can be challenging for engine 504 inJrRx device 500 since synchronization is conducted in the presence ofjamming signals. As shown in FIG. 5, the synchronization approachconducted by synchronization engine 504 (which may be executed by a JrRxdevice) may comprise three steps: (i) designing a spatialjamming-alleviation (JA) filter 510 (e.g., denoted as g) to alleviatethe jamming signals for the time-domain signal streams, (ii) employingvarious methods to estimate/correct the time and frequency offset overthe jamming-alleviated signal stream, and (iii) splitting the signalstreams into individual frames and compensate for their frequencyoffset. In this approach, JA filter 510 (e.g., filter g) is a M×1complex vector and is a primary component. JA filter 510 combines thesignal streams from different JrRx's antennas with the aim ofalleviating jamming signals by exploiting the spatial degrees of freedomprovided by the multiple antennas.

In some embodiments, JrRx device 500 can be configured with differenttypes of filters for JA filter 510. For example, in a first embodiment(‘Case I’), the disclosed subject matter may use one of the BJM filtersas a JA filter. In some embodiments, the BJM engine can generate afilter for each OFDM subcarrier and the disclosed subject matter may usethe centric BJM filter (i.e., P(0)) as the JA filter to alleviatejamming signals in the time domain. To illustrate, reference is now madeto FIG. 6, which depicts a diagram 600 illustrating jamming signals 602_(1 . . . K) and OFDM signal patterns according to an embodiment of thesubject matter described herein. Notably in FIG. 6, if a frame (e.g.,frame 604) was previously found in a given amount of time, the BJMfilter is used as the JA filter to alleviate the jamming signals.Specifically, the JA filter is designed by letting a JA filter g (e.g.,JA filter 510 in FIG. 5)=P(0), where P(0) is subcarrier 0's BJM filterin the previous frame. Note that subcarrier 0 is the centric subcarrierin their OFDM spectrum. Regarding the performance of this filter, thefollowing Lemma 2 is presented: If the channels between i) asender/jammer device and ii) a receiver device are frequency-flat andthe noise is negligible, then JA filter g=P(0) can completely cancel thejamming signals.

In particular, Lemma 2 shows the efficacy of the JA filter design in anideal scenario. Although the channels are not frequency-flat, thefrequency responses of neighboring OFDM subcarriers are highlycorrelated in practice. Therefore, filter P(0) can significantlyalleviate the jamming signals in the time domain at the receiver device.

In a second case (‘Case II’), the disclosed subject matter may use aleft-singular vector as a JA filter. Again, referring to diagram 600 inFIG. 6, if a frame was not found in a given amount of time, then aleft-singular vector (e.g., vector 608) of the signals is used as the JAfilter to alleviate the jamming signals. Specifically, the singularvalue decomposition (SVD) is conducted as follows:

$\begin{bmatrix}U & \Sigma & V\end{bmatrix} = {{svd}\left( {\sum\limits_{n = 1}^{N_{s}}{{y(n)}{y(n)}^{H}}} \right)}$where y(n) is the time-domain signal vector at the receiver device (seee.g., JrRx device 500 in FIG. 5), N_(s) is the number of signal samples,U is the left complex unitary matrix (M×M). U(i) can be denoted as theith column of matrix U, which is also known as the ith left-singularvector (e.g., vector 608). For each of the M left-singular vectors in U,the auto/cross correlation of the resulting signal U(i)^(H) y(t) for1≤i≤M is measured. Subsequently, the vector that results in the largestcorrelation value is selected as the JA filter g. In some embodiments,note that the left-singular vectors in the SVD formula above can bereplaced with the eigenvector of the signal correlation and theeigenvector will yield the same performance. Regarding the performanceof this JA filter, the following Lemma 3 can be formulated: If thechannels between sender/jammer and receiver are frequency-flat and thenoise is negligible, then there is at least one column of U that cancompletely cancel jamming signals.

In some embodiments, Algorithm 2 summarizes the disclosed process fordesigning JA filter 510 (e.g., JA filter g) in FIG. 5, where lines 2-3of Algorithm 2 (see below) correspond to the first case (‘Case I’) andlines 5-10 correspond to the second case (e.g., ‘Case II’) as describedabove. The worst-case computational complexity of this synchronizationalgorithm is M times that of a conventional synchronization algorithm.In real-world systems, Case I is dominant and, therefore, the complexityof synchronization module is similar to that of the conventionalsynchronization algorithm. Notably, the design of a JA filter g forsynchronization is detailed in Algorithm 2, which can be represented as:

 1: if A frame was found in a given amount of time then  2: Denote P(k)as subcarrier k's BJM filter in that frame;  3: g = P(0);  4: else  5:Compute the left unitary matrix U using SVD;  6: for i from 1 to M do 7: Compute the maximum correlation value of signal stream U(i)^(H)y(n), which we denote as c_(i) ;  8: end for  9: i_(m) = arg max_(1≤i≤M){c_(i)}; 10: g = U(i_(m)); 11: end if

In some embodiments, the disclosed subject matter may be configured toconduct jamming mitigation and channel equalization. As shown in FIG. 5,once a radio frame has been found and the frequency offset has beencorrected, the signal streams are fed to the FFT module 506, whichconverts each signal stream from the time domain to the frequencydomain. For each subcarrier of the resulting frequency-domain signals,the BJM algorithm can be utilized to mitigate jamming signals andequalize the channel distortion. Specifically, for subcarrier k,P=[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over (Y)}(l)^(H)]^(†)[Σ_(l=1)^(L){tilde over (Y)}(l){tilde over (Y)}(l)^(H)] is used to compute thesubcarrier's BJM filter P(k) and {circumflex over (X)}=P^(H)Y is used todecode the signal 9(k).

As indicated in P=[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(X)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over (Y)}(l)(l)^(H)], the design ofthe BJM filter needs pilot signals (e.g., reference signals). The morepilot signals that are available, the better the BJM filter performs.For each subcarrier, the BJM engine determines which pilot signals inthe preamble field of the source signal frame can be used for the BJMfilter design. As illustrated in FIG. 7, for the design of subcarrierk's BJM filter, the pilot signals are used not only on that subcarrierbut also on that subcarrier's neighboring subcarriers. This is possiblebecause the channels neighboring subcarriers (e.g., subcarriers 708_(k−2), 708 _(k−1), 708 _(k+1), and 708 _(k+2)) of subcarrier k 708 _(k)in FIG. 7 are highly correlated in real-world networks.

In some embodiments, P_(k) is denoted as the set of pilot signals thatare used for subcarrier k's BJM filter design. Based on Wi-Fi's framestructure 700 in FIG. 7, P_(k)={(l, k′): 1≤l≤4; k−2≤k′≤k+2}, where 1≤l≤4means the pilot OFDM symbols in the L-STF field 704 and L-LTF field 706(e.g., preamble fields), and k−2≤k′≤k+2 means the neighboring twosubcarriers. Then, based on P=[Σ_(l=1) ^(L){tilde over (Y)}(l){tildeover (X)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(X)}(l)^(H)], subcarrier k's BJM filter P(k) can be written as:

${P(k)} = {\left\lbrack {\sum\limits_{{({l,k^{\prime}})} \in P_{k}}{{Y\left( {l,k^{\prime}} \right)}{Y\left( {l,k^{\prime}} \right)}^{H}}} \right\rbrack^{\dagger}\left\lbrack {\sum\limits_{{({l,k^{\prime}})} \in P_{k}}{{Y\left( {l,k^{\prime}} \right)}{X\left( {l,k^{\prime}} \right)}^{H}}} \right\rbrack}$

where X(l, k′), (l, k′)∈P_(k), represents the pilot signals at thesender and Y(l, k′), (l, k′)∈P_(k), represents the received signalvector at the receiver, which includes both pilot signals and jammingsignals. After computing the BJM filter P(k), the {circumflex over(X)}=P(k)^(H)Y formula is used to decode the desired signals on eachsubcarrier of all the OFDM symbols in the frame. In some embodiments,legacy short training field 704 may have two orthogonal frequencydivisional multiplexing (OFDM) symbols and the legacy long trainingfield 706 has two identical OFDM symbols, which are used forsynchronization and channel estimation by the JrRx device.

In some embodiments, the JrRx device is depicted as enabling legitimatecommunications in a Wi-Fi MIMO network with one or multiple jammingemitters (e.g., as shown in FIG. 1). Further, the operations at theWi-Fi receivers and the subsequent operations at the Wi-Fi transmittersare presented. Collectively, these operations constitute an anti-jammingscheme that enables jamming-resistant communications in a networkenvironment.

In some embodiments, the disclosed subject matter is configured toconduct jamming mitigation at a wireless receiver, e.g., a JrRx device.Although the wireless network has many devices (e.g., access point anduser devices), only one of the devices is actively transmitting signalsat one moment due to the media access control. Hence, the communicationin the wireless network under jamming attacks can be modeled as thejamming problem that is presented in FIG. 4. As described above, eachwireless user device (e.g., sender device and receiver device) isassumed to have more antennas than the jammers present. Notably, theJrRx can be configured to successfully decode the signals from thesender in the presence of jamming signals.

In some embodiments, the disclosed subject matter is configured toconduct carrier sensing at the Wi-Fi transmitter or sending device. In awireless network, a CSMA mechanism is used for media access control.Specifically, if a Wi-Fi device wants to transmit, the transmittingdevice first conducts carrier sensing to assess whether the channel isidle. If the channel is determined to be idle, the transmitting devicewill defer and wait for a random amount of time. Otherwise, thetransmitting device will use the channel for data transmission.

In some embodiments, a wireless device (e.g., a Wi-Fi device) isconfigured to conduct carrier sensing in the presence of jammingsignals. Considering the robustness of autocorrelation and/or crosscorrelation of a signal preamble field (e.g., Wi-Fi preamble field) inthe presence of jamming, the preamble detection method is employed forcarrier sense at each Wi-Fi device. For example, each Wi-Fi device actsas a receiver before transmitting, and uses the information from asynchronization algorithm (e.g., as described above) to assess whetherthere is a Wi-Fi signal present in the channel. If a Wi-Fi frame wasfound by the time synchronization algorithm in a given and/or predefinedamount of time, then the channel is considered ‘busy’ (e.g., not idle)and the Wi-Fi device defers and waits for a random amount of time beforeits next attempt. Otherwise, the channel is considered idle and theWi-Fi device uses the channel for data transmission.

FIG. 8A is an image of an experimental setup in a testing environmentaccording to an embodiment of the subject matter described herein. Forexample, a prototype of the JrRx can be constructed using USRP N210devices, OctoClock-G CDA-2990, a Gigabit-Switch, and a GNURadio softwarepackage, as shown in FIG. 8A. Further, a prototype of one sender deviceusing one USRP N210 device and GNURadio has also been similarlyconstructed. The sender device and the JrRx run a simplified PHY layerof 802.11n in legacy mode using the frame structure 700 depicted in FIG.7. For example, each OFDM symbol has 64 subcarriers, with 52 of thesubcarriers being used for payloads. Further, QPSK modulation can beused for data transmission. Due to the hardware limitations, each USRPN210 at the sender device and JrRx is configured to span a 5 MHz channelby setting the decimation rate to 20 while the carrier frequency isconfigured to 2.4 GHz.

In some embodiments, a prototype of three jammers using three USRP N210devices and GNURadio is built. The waveform, spectrum, and power of eachjammer device's radio signal can be configured as needed. For example,FIG. 8B is an image 800 of the positioning of a sender device and jammerdevices in a testing environment according to an embodiment of thesubject matter described herein. More specifically, the sender deviceand the three jammer device are shown in FIG. 8B.

In some experimental scenarios, the performance of JrRx is evaluated inthree cases as shown in FIGS. 9A-9C. In each case, the sender device andjammer devices are placed at location “A” and the receiver device (JrRxdevice) is placed at location “B” in the example floor layout 806 shownin FIG. 8C. Specifically, FIG. 8B shows a photograph of an examplephysical placement of the sender device and the jammer devices atlocation “B” as indicated in floor layout 806. As shown, the jammersdevices can be placed closely to the sender device. Such a placement andconfiguration leads to one of the most destructive jamming attacks.

In some embodiments, the sender device's transmit power is fixed to 0dBm and each jammer device's power can be adjusted from 0 dBm to 20 dBm.Notably, the spectrum of jamming signals fully covers that of thelegitimate signals.

In some embodiments, various performance metrics can be used. Forexample, the post signal-to-jamming-plus-noise ratio (pSJNR) can be usedas the performance metric to assess the performance of the JrRx.Mathematically, pSJNR=10 log₁₀(E(|X|²)/E(|X−{circumflex over (X)}|²)),where X is the original signal at the sender and {circumflex over (X)}is the estimated signal at the JrRx. Once the pSJNR is measured at theJrRx, the Raw-BER (e.g., BER without channel code) of the QPSK datatransmission can be inferred by Raw-BER=2Q(√{square root over(γ)})−Q²(√{square root over (γ)}), where Q(⋅) is a Q-function and γ isthe linear value of

${pSJNR}\mspace{14mu}{\left( {{e.g.},{\gamma = 10^{\frac{pSJNR}{10}}}} \right).}$In real-world wireless systems (e.g., Wi-Fi and LTE), Raw-BER 10⁻²,which corresponds to pSJNR 8.2 dB according to the above formula, issufficient for the receiver to successfully decode the signal.Therefore, in some embodiments, pSJNR 8.2 dB can be used as the pSJNRthreshold of successful data reception at the JrRx device.

As a case study, the performance of JrRx may be explored in the networkas shown in FIG. 9A, which is a block diagram illustrating an exemplarysignal jamming model involving a single jamming device in amultiple-input and multiple-output (MIMO) environment according to anembodiment of the subject matter described herein. More specifically,FIG. 9A depicts a wireless network 900 that includes a sender device902, a jammer device 906, and a receiving JrRx device 904. Notably, eachof the sender device 902 and jammer device 906 has one antenna and theJrRx device 904 has two antennas. The sender device's transmit power isfixed to 0 dBm and the jammer device's transmit power is set to {0, 10,20} dBm, respectively.

The performance of the proposed synchronization algorithm can beevaluated in the JrRx device. Recall that the core of thesynchronization algorithm includes two jamming-alleviation filters(JAF), e.g., a BJM filter P(0) and a left-singular vector U(i). Theimpacts of these filters are evaluated on the cross-correlation of thereceived signals, respectively. In some experiments, thecross-correlation results are obtained by correlating the L-LTF signalwith a local L-LTF signal (e.g., preamble signals).

FIG. 9B is a block diagram illustrating an exemplary signal jammingmodel involving a pair of jamming devices in a multiple-input andmultiple-output (MIMO) environment according to an embodiment of thesubject matter described herein. More specifically, FIG. 9B depicts awireless network 901 that includes a sender device 902, jammer devices9061 and 9062, and a receiving JrRx device 907. Notably, each of thesender device 902 and jammer devices 906 has one antenna and the JrRxdevice 907 has three (or more) antennas. Although introduced here, FIG.9B is described in further detail below.

FIG. 9C is a block diagram illustrating an exemplary signal jammingmodel involving three jamming devices in a multiple-input andmultiple-output (MIMO) environment according to an embodiment of thesubject matter described herein. More specifically, FIG. 9B depicts awireless network 903 that includes a sender device 902, jammer devices9061, 9062, and 9063, and a receiving JrRx device 908. Notably, each ofthe sender device 902 and jammer devices 906 has one antenna and theJrRx device 908 has four (or more) antennas. Although introduced here,FIG. 9C is described in further detail below.

FIG. 10 illustrates a plurality of graphs depicting the performance oftwo jamming-alleviation filters (JAF) in the synchronization algorithmat various transmitting powers according to an embodiment of the subjectmatter described herein. More specifically, FIG. 10 presents the impactof the two JAFs on the cross-correlation results of the received signalsat the JrRx device. For example, graphs 1001-1003 present thecross-correlation results when the jammer device's transmit power is 0dBm. Likewise, graphs 1004-1006 present the cross-correlation resultswhen the jammer device's transmit power is 10 dBm. Further, graphs1007-1009 present the cross-correlation results when the jammer device'stransmit power is 20 dBm. Inspecting graphs 1001-1003 in the first rowof FIG. 10 when the jammer device's transmit power is 0 dBm, it isevident that (e.g., by comparing graph 1001 and graph 1002) by usingleft-singular vector U(i) as a JAF can significantly improve theperformance of the synchronization algorithm. Comparing graph 1001 andgraph 1003, it is further evident that using BJM filter P(0) as JAF cansignificantly improve the performance of the synchronization algorithmas well. The same phenomenon can be observed in graphs 1004-1006 in thesecond row (e.g., when the jammer device's transmit power is 10 dBm) andgraphs 1007-1009 in the third row of FIG. 10 (e.g., when the jammerdevice's transmit power is 20 dBm). Based on the above observations, itcan be concluded that the proposed synchronization algorithm is able toachieve synchronization in the presence of jamming attacks.

FIGS. 11A-11D illustrate a plurality of constellation diagrams of thedecoded symbols at the JrRx device when subjected to different transmitpowers from the jammer device according to an embodiment of the subjectmatter described herein. In some instances, the performance of BJMAlgorithm in the JrRx device can be evaluated. FIGS. 11A-11D present theconstellation diagram of the decoded symbols at the JrRx. For example,FIG. 11A presents the constellation diagram 1101 when there is nojamming attack present. In this scenario, the pSJNR is 15.3 dB, whichcorresponds to Raw-BER 5.8E-9. FIG. 11B presents the constellationdiagram 1102 when the jammer device's transmit power is 0 dBm. In thiscase, the pSJNR is 14.5 dB, which corresponds to Raw-BER 1.1E-7. FIG.11C presents the constellation diagram 1103 when jammer device'stransmit power is 10 dBm. In this case, the pSJNR is 13.9 dB, whichcorresponds to Raw-BER 7.3E-7. FIG. 11D presents the constellationdiagram 1104 when jammer device's transmit power is 20 dBm. In thiscase, the pSJNR is 12.7 dB, which corresponds to Raw-BER 1.6E-5.Comparing constellation diagram 1104 to constellation diagram 1101, itis evident that the pSJNR degradation is less than 3 dB when the jammingsignal is 20 dB stronger than the desired signal. This indicates therobustness of the disclosed BJM algorithm.

In some instances, the impact of jamming waveforms can be evaluated. Forexample, the destructiveness of different jamming waveforms in thenetworks (e.g., networks 900, 901 and 903) as shown in FIGS. 9A-9C canbe examined. In this experimental scenario, four jamming attacks areconsidered, including (i) a full-spectrum jamming attack, (ii) ahalf-spectrum jamming attack, (iii) a single-frequency jamming attack(e.g., a cosine jamming signal), and (iv) a rectangular-waveform jammingattack (e.g., sinc-shaped jamming spectrum). FIG. 12 presents a graph1200 that illustrates the performance of the JrRx device under thesefour types of jamming attacks. It is evident that the pSJNR at the JrRxdevice is greater than 8.2 dB and thus the JrRx device can successfullydecode the desired signal under the four jamming attacks. By inspectingFIG. 12, another observation can be made. Notably, the single-frequencyjamming attack is the most destructive attack among the four indicatedjamming attacks. Raw experimental data has been analyzed and hasindicated that the destructiveness of single-frequency jamming attack isattributed to its adverse effect on the frequency synchronization (e.g.,estimating the frequency offset at the JrRx device). Namely, when thejamming signal is a strong cosine waveform, the JrRx device can havedifficulty to accurately estimate the frequency offset. Accordingly, thepSJNR degrades accordingly.

The performance of the JrRx device can be examined under differentjamming powers in the three cases as shown in FIGS. 9A-9C. For example,in some embodiments involving a single jammer device, graph 1300 in FIG.13 illustrates the experimental results that were measured in thenetwork with one jammer device (as shown in FIG. 9A). In graph 1300 ofFIG. 13, “−Inf” on x-axis indicates that the network has no jammingsignal. From the experimental results, it is evident that when the JrRxdevice has two or more antennas, the JrRx device successfully decodesthe desired signal from the sender device (e.g., pSJNR≥8.2 dB). When thejamming power from −Inf is increased to 20 dBm, the pSJNR degradation atthe JrRx device is less than 5 dB. This indicates the robustness of theBJM algorithm in the JrRx device.

Similarly, graph 1400 in FIG. 14 presents the experimental results thatwere measured in the network with two jammer devices (as shown FIG. 9B).Since there are two jammer devices in the network, the total jammingpower amounts to the sum of the signal power from the two jammerdevices. It is evident that when the JrRx device has three or moreantennas, the JrRx device can successfully decode the desired signalfrom the sender device (e.g., pSJNR≥8.2 dB), even if the jamming signalis 20 dB stronger than the desired signal.

Further, graph 1500 of FIG. 15 presents the experimental results thatwere measured in the network with three jammers devices (as shown inFIG. 9C). It is evident that when the JrRx device has four antennas, theJrRx device successfully decodes the desired signal from the sender(e.g., pSJNR≥8.2 dB), even if the jamming signal from each jammer deviceis 17 dB stronger than the desired signal. Note that there are threejammer devices in the network so there is an additional 4.8 dB for thetotal jamming power.

Observations may be summarized based on the experimental results. Forthe conventional receiver, the receiver device cannot successfullydecode the desired signal when the jamming signal has similar or largerpower than the desired signal. In contrast, the disclosed JrRx device iscapable of successful decoding the desired source signal, as long as theJrRx device has more antennas than the jammers, even if the jammingsignals are 20 dB stronger than the desired source signals.

The disclosed subject matter describes the first practical anti-jammingsolution that can address multiple high-power and broadband jammingattackers in wireless MIMO networks. The core of the solution is theJrRx device, which has two key components: i) a jamming-resilientsynchronization algorithm and ii) a BJM algorithm. In some embodiments,the BJM algorithm can mitigate jamming signals without the need of anychannel information. Further, the synchronization algorithm canaccomplish timing and frequency synchronization in the presence ofstrong jamming. Experimental results show that (i) the JrRx device isrobust to various jamming signals (e.g., full-spectrum jamming,half-spectrum jamming, single-frequency jamming, andrectangular-waveform jamming) and (ii) as long as the JrRx device hasmore antennas than the jammers, it can successfully decode the signalsfrom the sender, even in the scenarios where the jamming signals are 20dB stronger than the desired signals.

FIG. 16 is a block diagram illustrating an exemplary JrRx device 1600according to an embodiment of the subject matter described herein. Asshown in FIG. 16, JrRx device 1600 may include one or more processors1602, such as a central processing unit (e.g., a single core or multipleprocessing cores), a microprocessor, a microcontroller, a networkprocessor, an application-specific integrated circuit (ASIC), or thelike. JrRx device 1600 may also include memory 1604. Memory 1604 maycomprise random access memory (RAM), flash memory, a magnetic diskstorage drive, and the like. In some embodiments, memory 1604 may beconfigured to store a synchronization engine 1608 and blind jammingmitigation engine 1610. Notably, synchronization engine 1608 stored inmemory 1604 can perform various synchronization, frame splitting, and/oroffset correction functionalities for JrRx device 1600 when executed byone or more processors 1602. Likewise, BJM engine 1610 stored in memory1604 can perform various jamming alleviation and signal jamming and/orcanceling functionalities for JrRx device 1600 when executed by one ormore processors 1602.

FIG. 17 is a flow chart illustrating an exemplary process or method 1700for utilizing a jamming-resistant receiver device according to anembodiment of the subject matter described herein. In some embodiments,method 1700 depicted in FIG. 17 is an algorithm stored in memory thatwhen executed by a hardware processor performs one or more of blocks1702-1708.

In block 1702, method 1700 includes receiving a plurality of individualsubcarrier signals that comprises separate signal portions of a combinedsignal stream, wherein the combined signal stream is a combinationformed by a source signal stream from a sender device and one or moreinterfering jamming signals from a plurality of unknown jammer devices.In some embodiments, the plurality of individual subcarrier signals isreceived by a BJM engine in a JrRx device from a resident FFT module.Notably, the subcarrier signals are the result of processing a combinedsignal stream by a synchronization engine in the JrRx device as well assubsequent processing by the FFT module.

In block 1704, method 1700 includes computing a respective plurality ofBJM filters for the plurality of individual subcarrier signals in theabsence of channel information corresponding to the interfering jammingsignals In some embodiments, the JrRx device is configured utilize itsBJM engine to calculate a BJM filter (e.g., P=[Σ_(l=1) ^(L){tilde over(Y)}(l){tilde over (X)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over(Y)}(l){tilde over (X)}(l)^(H)]) for each of the plurality ofsubcarriers.

In block 1706, method 1700 includes applying the plurality of BJMfilters to the respective plurality of individual subcarrier signals todecode data packets of the plurality of individual subcarrier signals inorder to produce a plurality of source signal stream portions as decodedoutput. In some embodiments, the BJM engine in the JrRx device providesthe plurality of subcarriers as input to the respective plurality of BJMfilters and obtains decoded data packets corresponding to differentportions of the original source signal stream as output.

In block 1708, method 1700 includes recovering the source signal streamby combining the decoded output from each of the plurality of BJMfilters. In some embodiments, the JrRx device and/or the BJM engine isconfigured to combine the decoded data packets to recreate the originalsource signal stream transmitted by the legitimate sender device.

Advantages of the subject matter described herein include a jammingresistant solution for preserving legitimate wireless communicationsagainst constant wideband jamming attacks by leveraging multipleantennas on wireless user devices. In particular, the disclosed jammingmitigation algorithm can cancel the interfering signals from the jammerdevice(s) and recover the desired signals transmitted from a legitimatesender device. Unlike existing jamming mitigation algorithms thatrequire and rely on the availability of accurate jamming channel ratioinformation, the disclosed jamming mitigation algorithm does not requireany channel information or jamming device information of any kind.Further, the disclosed subject matter also affords a jamming resistantreceiver device that can decode data packets from a legitimatetransmitter in the presence of interfering signals originating frommultiple unknown jammer devices. As such, the jamming resistant receiverdevice and/or the jamming mitigation algorithm as described hereinimproves the technological field of wireless device communications byproviding a means that is capable of canceling high-powered widebandjamming attacks in a more efficient manner.

In some embodiments, the disclosed subject matter includes and enhancedPHY design for a wireless receiver that can defend against not onlyconstant jamming attacks but also reactive and proactive high-poweredwideband jamming attacks. For example, FIG. 18 illustrates a signalframe format 1802 of an OFDM signal, where L-STF is the legacy shorttraining field 1804, L-LTF is the legacy long training field 1806, andL-SIG is the legacy signal field 1808, and RTF is the rear trainingfield 1810. As used herein, fields 1804-1808 may be referenced aspreamble fields. Utilizing this signal frame format, the disclosedsubject matter affords a wireless JrRx device that can successfullydecode the OFDM signals from the transmitter in the presence of unknownwide-band jamming signals. Notably, the receiver's jamming cancellationcapability is 1 to up to 30 decibels.

FIG. 19 is a block diagram of an exemplary architecture of ajamming-resistant receiver (JrRx) device 1900 according to an embodimentof the subject matter described herein in some embodiments, the JrRxdevice 1900 may be equipped with a synchronization engine 1902, which isconfigured with at least two functionalities: timing synchronizationfunctionality and a frequency synchronization functionality. In thecontext of synchronization engine 1902 of JrRx device 1900, timingsynchronization involves the searching for the burst frames byexploiting autocorrelation or cross-correlation up the signal stream inthe time domain. Likewise, frequency synchronization conducted bysynchronization engine 1902 involves estimating and correcting thefrequency offset existing between the transmitter device and thereceiver device.

Notably, synchronization in the JrRx device 1900 is a challenging tasksince the synchronization must be done in the presence of jammingsignals. In some embodiments, the synchronization engine 1902 in FIG. 19includes three components: a spatial jamming alleviation filter 1903that is used to alleviate the jamming signals for the time domain signalstreams, a synchronization algorithm component 1905 that is used toestimate the timing and frequency offsets, and a frame detection andcarrier frequency offset correction component 1904. In some embodiments,a jamming alleviation (JA) filter 1903 is a key component in thesynchronization engine 1902. Construction of the JA filter 1903 can beachieved through sophisticated manipulations of the jamming migrationfilter (e.g., JMCE component 1908) and the left singular vectors of theincoming signals.

As shown in FIG. 19, the JrRx device 1900 also includes a jammingmigration and channel equalization (JMCE) component 1908. For example,once a radio frame has been found and the frequency offset has beencorrected by the synchronization engine 1902, the signal streams are fedto an FFT module 1906, which converts each signal stream from the timedomain to frequency domain. For each subcarrier of the resultingfrequency domain signals, JrRx device 1900 utilizes a jamming mitigationalgorithm to cancel the jamming signals and equalize any channeldistortion. Specifically, for each subcarrier, the JrRx device computesa JMCE filter and uses this filter to estimate the original signal. Inorder to compute the JMCE filters, the JrRx device leverages thereference signals in the L-STF, L-LTF, and RTF fields. Notably, theadaptive jamming mitigation algorithm used to construct the JMCE filtermay achieve up to 30 decibels jamming mitigation.

In some embodiments, the JrRx device has been demonstrated tosuccessfully decode a source signal from a transmitting device in theface of unknown jamming attacks. The JrRx device displays theconstellation diagram of the decoded video signal from the transmitterand can play the video smoothly. The demonstration participants cancontrol the parameters (e.g., the bandwidth, power, waveform, carrierfrequency, etc.) of the jamming signal using the interface controlpanel. The demonstration participants can also observe the impact of thejamming attacks on the performance of the JrRx device through theconstellation diagram and the played video. The demonstrationparticipants may also see that the JrRx device can successfully decodethe video signals from the transmitter and play a video stream even ifthe jamming signal is 20 decibels stronger than the useful signal.

It will be understood that various details of the presently disclosedsubject matter can be changed without departing from the scope of thepresently disclosed subject matter. Furthermore, the foregoingdescription is for the purpose of illustration only, and not for thepurpose of limitation.

REFERENCES

All references listed in the instant disclosure, including but notlimited to all patents, patent applications and publications thereof,scientific journal articles, and database entries are incorporatedherein by reference in their entireties to the extent that theysupplement, explain, provide a background for, or teach methodology,techniques, and/or embodiments employed herein.

-   [1] W. Xu, W. Trappe, Y. Zhang, and T. Wood, “The feasibility of    launching and detecting jamming attacks in wireless networks,” in    ACM MobiHoc, pp. 46-57, 2005.-   [2] W. Shen, P. Ning, X. He, and H. Dai, “Ally friendly jamming: How    to jam your enemy and maintain your own wireless connectivity at the    same time,” in IEEE Symposium on Security and Privacy, pp. 174-188,    2013.-   [3] M. K. Hanawal, M. J. Abdel-Rahman, and M. Krunz, “Joint    adaptation of frequency hopping and transmission rate for    anti-jamming wireless systems,” IEEE Transactions on Mobile    Computing, vol. 15, no. 9, pp. 2247-2259, 2016.-   [4] W. Xu, T. Wood, W. Trappe, and Y. Zhang, “Channel surfing and    spatial retreats: Defenses against wireless denial of service,” in    ACM Workshop on Wireless security, pp. 80-89, 2004.-   [5] V. Navda, A. Bohra, S. Ganguly, and D. Rubenstein, “Using    channel hopping to increase 802.11 resilience to jamming attacks,”    in IEEE INFOCOM, pp. 2526-2530, 2007.-   [6] M. Strasser, C. Popper, S. Capkun, and M. Cagalj,    “Jamming-resistant key establishment using uncoordinated frequency    hopping,” in IEEE Symposium on Security and Privacy, pp. 64-78,    2008.-   [7] Q. Wang, P. Xu, K. Ren, and X.-Y. Liu, “Delay-bounded adaptive    UFH-based anti-jamming wireless communication,” in IEEE INFOCOM, pp.    1413-1421, 2011.-   [8] Y. Liu, P. Ning, H. Dai, and A. Liu, “Randomized differential    DSSS: Jamming-resistant wireless broadcast communication,” in IEEE    INFO-COM, pp. 1-9, 2010.-   [9] A. Liu, P. Ning, H. Dai, Y. Liu, and C. Wang, “Defending    DSSS-based broadcast communication against insider jammers via    delayed seed-disclosure,” in ACM ACSAC, pp. 367-376, 2010.-   [10] T. Jin, G. Noubir, and B. Thapa, “Zero pre-shared secret key    establishment in the presence of jammers,” in ACM MobiHoc, pp.    219-228, 2009.-   [11] S. Gollakota, F. Adib, D. Katabi, and S. Seshan, “Clearing the    RF smog: Making 802.11n robust to cross-technology interference,” in    ACM SIGCOMM, vol. 41, pp. 170-181, 2011.-   [12] T. D. Vo-Huu, E.-O. Blass, and G. Noubir, “Counter-jamming    using mixed mechanical and software interference cancellation,” in    ACM WiSec, pp. 31-42, 2013.-   [13] Q. Yan, H. Zeng, T. Jiang, M. Li, W. Lou, and Y. T. Hou,    “Jamming resilient communication using MIMO interference    cancellation,” IEEE Transactions on Information Forensics and    Security, vol. 11, no. 7, pp. 1486-1499, 2016.-   [14] D. Tse and P. Viswanath, Fundamentals of wireless    communication. Cambridge university press, 2005.-   [15] A. B. Awoseyila, C. Kasparis, and B. G. Evans, “Robust    time-domain timing and frequency synchronization for OFDM systems,”    IEEE Trans-actions on Consumer Electronics, vol. 55, no. 2, 2009.-   [16] Y.-C. Wu, K.-W. Yip, T.-S. Ng, and E. Serpedin,    “Maximum-likelihood symbol synchronization for ieee 802.11a wlans in    unknown frequency-selective fading channels,” IEEE Transactions on    Wireless Communica-tions, vol. 4, no. 6, pp. 2751-2763, 2005.-   [17] E. Research, “USRP N210,”    www.ettus.com/product/details/UN210-KIT [Online; accessed 8 Mar.    2017].-   [18] E. Blossom, “GNU radio: Tools for exploring the radio frequency    spectrum,” Linux journal, vol. 2004, no. 122, p. 4, 2004.-   [19] J. G. Proakis, “Digital communications,” McGraw-Hill, New York,    1995.

What is claimed is:
 1. A method comprising: receiving, by a blindjamming mitigation (BJM) engine in a jamming-resistant receiver (JrRx)device, a plurality of individual subcarrier signals that comprisesseparate signal portions of a combined signal stream, wherein thecombined signal stream is a combination formed by a source signal streamfrom a sender device and one or more interfering jamming signals from aplurality of unknown jammer devices; computing, by the BJM engine, arespective plurality of BJM filters for the plurality of individualsubcarrier signals in the absence of channel information correspondingto the interfering jamming signals; applying, by the BJM engine, theplurality of BJM filters to the respective plurality of individualsubcarrier signals to decode data packets of the plurality of individualsubcarrier signals as decoded output, wherein each of the plurality ofBJM filters comprises a linear spatial filter that is configured toprocess pilot signals from the sender device such that informationpertaining to the one or more jamming signals or the plurality ofunknown jamming devices is unnecessary to generate the decoded output;and recovering, by the BJM engine, the source signal stream by combiningthe decoded output from each of the plurality of BJM filters.
 2. Themethod of claim 1 wherein recovering the source signal stream includesequalizing a channel using the one or more of the plurality of BJMfilters to decode the source signal.
 3. The method of claim 1 whereincomputing one or more of the BJM filters includes determining aplurality of pilot signals or reference signals included in preamblefields of a frame of the source signal stream that originates from thesender device.
 4. The method of claim 1 wherein computing one or more ofthe plurality of BJM filters is conducted when jamming channelinformation of the one or more interfering jamming signals isunavailable or unknown.
 5. The method of claim 1 wherein each of theJrRx device and the sender device includes a number of antennas thatexceeds a sum of antennas associated with the plurality of unknownjammer devices.
 6. The method of claim 1 wherein the plurality ofindividual subcarrier signals includes a plurality of frequencydivisional multiplexing (OFDM) subcarriers.
 7. The method of claim 1wherein each of the plurality of BJM filters includes a BJM filter thatis represented as P=[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(Y)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over (Y)}(l){tilde over(Y)}(l)^(H)], where (⋅)^(†) is a pseudo-inverse operator, wherein {tildeover (Y)}(l) represents pilot signals received at the receiver deviceand {tilde over (X)}(l) represents pilot signals at the sender device.8. A jamming-resistant receiver (JrRx) device comprising: at least oneprocessor and memory; and a blind jamming mitigation (BJM) engine storedin the memory and when executed by the at least one processor isconfigured for receiving a plurality of individual subcarrier signalsthat comprises separate signal portions of a combined signal stream,wherein the combined signal stream is a combination formed by a sourcesignal stream from a sender device and one or more interfering jammingsignals from a plurality of unknown jammer devices, computing arespective plurality of BJM filters for the plurality of individualsubcarrier signals in the absence of channel information correspondingto the interfering jamming signals, applying the plurality of BJMfilters to the respective plurality of individual subcarrier signals todecode data packets of the plurality of individual subcarrier signals asdecoded output, wherein each of the plurality of BJM filters comprises alinear spatial filter that is configured to process pilot signals fromthe sender device such that information pertaining to the one or morejamming signals or the plurality of unknown jamming devices isunnecessary to generate the decoded output, and recovering the sourcesignal stream by combining the decoded output from each of the pluralityof BJM filters.
 9. The JrRx device of claim 8 wherein recovering thesource signal stream includes equalizing a channel using one or more ofthe plurality of BJM filters to decode the source signal.
 10. The JrRxdevice of claim 8 wherein a synchronization engine is configured fordetermining a plurality of pilot signals or reference signals includedin preamble fields of a frame in the source signal stream thatoriginates from the sender device.
 11. The JrRx device of claim 8wherein the BJM engine is further configured for computing a JA filterwhen jamming channel information of the one or more interfering jammingsignals is unavailable or unknown.
 12. The JrRx device of claim 8wherein each of the JrRx device and the sender device includes a numberof antennas that exceeds a sum of antennas associated with the pluralityof unknown jammer devices.
 13. The JrRx device of claim 8 wherein theplurality of individual subcarrier signals includes a plurality offrequency divisional multiplexing (OFDM) subcarriers.
 14. The JrRxdevice of claim 8 wherein each of the plurality of BJM filters includesa BJM filter that is represented as P=[Σ_(l=1) ^(L){tilde over(Y)}(l){tilde over (Y)}(l)^(H)]^(†)[Σ_(l=1) ^(L){tilde over(Y)}(l){tilde over (Y)}(l)^(H)], where (⋅)^(†) is a pseudo-inverseoperator, wherein {tilde over (Y)}(l) represents pilot signals receivedat the receiver device and {tilde over (X)}(l) represents pilot signalsat the sender device.
 15. A non-transitory computer readable mediumhaving stored thereon executable instructions that when executed by aprocessor of a computer controls the computer to perform stepscomprising: receiving, by a BJM engine, a plurality of individualsubcarrier signals that comprises separate signal portions of a combinedsignal stream, wherein the combined signal stream is a combinationformed by a source signal stream from a sender device and one or moreinterfering jamming signals from a plurality of unknown jammer devices;computing, by the BJM engine, a respective plurality of BJM filters forthe plurality of individual subcarrier signals in the absence of channelinformation corresponding to the interfering jamming signals; applying,by the BJM engine, the plurality of BJM filters to the respectiveplurality of individual subcarrier signals to decode data packets of theplurality of individual subcarrier signals as decoded output, whereineach of the plurality of BJM filters comprises a linear spatial filterthat is configured to process pilot signals from the sender device suchthat information pertaining to the one or more jamming signals or theplurality of unknown jamming devices is unnecessary to generate thedecoded output; and recovering, by the BJM engine, the source signalstream by combining the decoded output from each of the plurality of BJMfilters.
 16. The non-transitory computer readable medium of claim 15wherein recovering the source signal stream includes equalizing achannel using the one or more of the plurality of BJM filters to decodethe source signal.
 17. The non-transitory computer readable medium ofclaim 15 wherein computing one or more of the plurality of BJM filtersincludes determining a plurality of pilot signals or reference signalsincluded in preamble fields of a frame of the source signal stream thatoriginates from the sender device.
 18. The non-transitory computerreadable medium of claim 15 wherein computing one or more of theplurality of BJM filters is conducted when jamming channel informationof the one or more interfering jamming signals is unavailable orunknown.
 19. The non-transitory computer readable medium of claim 15wherein each of the JrRx device and the sender device includes a numberof antennas that exceeds a sum of antennas associated with the pluralityof unknown jammer devices.
 20. The non-transitory computer readablemedium of claim 15 wherein the plurality of individual subcarriersignals includes a plurality of frequency divisional multiplexing (OFDM)subcarriers.